But Federer is #1 because the rankings are based on the past 52 weeks, not just this year. Especially due to that amazing run he had at the end of 2011. In a month, he won Basel, Paris and the WTF and grabbed 2500 points.

Oracle1 - Thanks for the information - I stand corrected in relation to the race points this year. I thought Federer was ahead in this regard too. In any event, with so many points to defend for Basel, Paris-Bercy & the WTF, Federer is likely to lose the singles ranking lead too.

To those that know these things, what is the likelihood of Federer being able to end the year as number 1? What would he need to do?

IF Roger wins the US Open.... (in the 'minds' of many)...he would probably be the #1 player regardless of how the points pan out at the end of the year. Just like people (right now) think Serena is the 'real' #1 women's player. If Roger could win 2 slams, have won master's titles.... heck, he probably would deserve it. But it's a long season to go. I would said if Roger keeps his current form, he should do well in the indoor season as he is one of the best indoor players on tour (remember all the talk about 'the roof' 'the roof'! lol)

Yeah, Dallas is right - if Roger wins the US Open, he would be the favourite for the year end #1. Last year, he lost in the semis, so he earned only 720 points. So if he could win and earn the full 2000 this year, that would be a massive gain for him of 1280 points. Assuming Djokovic reaches the final, he would earn 1200 points, thereby losing 800 points in comparison to last year. Hence, a total points swing of 1280 + 800 = 2080. He already has a lead of almost 900 points, so winning the US Open would virtually ensure him the year end #1.

If Djokovic beats him in the final, Federer would still gain 480 points from last year, giving him an overall lead of 1375 points. Djokovic could grab the year end #1 if Federer underperforms at Shanghai, Paris or London.

If Murray beats Federer in the semis and Djokovic wins the final, the situation would remain the same as of now. Federer would still have a lead of 895 points, and it would be easier for Djokovic to overtake him at Shanghai or Paris.

If Murray beats Federer in the semi AND Djokovic in the final, he will become #3 while the gap between Federer and Djokovic would widen to 1695 points.